stack traces in the brush editor

after 35 thousand years it's finally here
good erro message

static/haku.js

@@ -244,7 +244,7 @@ export class Haku {
         w2.haku2_vm_destroy(this.#pVm2);
         w2.haku2_defs_destroy(this.#pDefs2);
         w2.haku2_limits_destroy(this.#pLimits2);
-        w2.haku_dealloc(this.#bytecode2.ptr);
+        freeString2(this.#bytecode2);
     }
 
     setBrush(code) {
@@ -332,12 +332,49 @@ export class Haku {
         return exn;
     }
 
+    #stackTrace() {
+        let count = w2.haku2_vm_stackframe_count(this.#pVm2);
+        let trace = [];
+        for (let i = 0; i < count; ++i) {
+            let isSystem = w2.haku2_vm_stackframe_is_system(this.#pVm2, i) != 0;
+            let pc = w2.haku2_vm_stackframe_pc(this.#pVm2, i);
+
+            let span = null;
+            if (!isSystem && pc > 0) {
+                // NOTE: We find the span at (pc - 1), because stack frames' program counters are
+                // situated at where control flow _ought_ to return, and not where the function call
+                // is located. Therefore, to pull the program counter back into the function call,
+                // we subtract 1.
+                let pSpan = w.haku_bytecode_find_span(this.#pInstance, Math.max(0, pc - 1));
+                if (pSpan != 0) {
+                    span = {
+                        start: w.haku_span_start(pSpan),
+                        end: w.haku_span_end(pSpan),
+                    };
+                }
+            }
+
+            trace.push({
+                isSystem,
+                pc,
+                span,
+                functionName: readString(
+                    memory2,
+                    w2.haku2_vm_stackframe_function_name_len(this.#pVm2, i),
+                    w2.haku2_vm_stackframe_function_name(this.#pVm2, i),
+                ),
+            });
+        }
+        return trace;
+    }
+
     #exceptionResult() {
         return {
             status: "error",
             errorKind: "exception",
             description: "Runtime error",
             message: this.#exceptionMessage(),
+            stackTrace: this.#stackTrace(),
         };
     }